1. Field of Invention
The invention relates to a control unit of an automatic transmission. More particularly, the invention relates to a control unit that combines an electronic control device for speed-shift control and a position detecting switch. The control unit is disposed on the main body of an automatic transmission and is used for detecting range positions chosen by a driver during a selecting operation.
2. Description of Related Art
Conventional automatic transmissions are designed to control a hydraulic pressure control device incorporated into the main body of the transmission. The conventional transmissions use an electronic control device to automatically perform the necessary speed-shift within a range selected while driving. The main body of the automatic transmission is connected to the engine of a vehicle and installed in an engine compartment. The electronic control device, needing to be located in an ideal temperature environment, is placed separate from the engine, such as, for example, in a passenger compartment.
As separate components, the automatic transmission main body and the electronic control device are subject to thorough quality control. Even when they are connected, quality control is required because the automatic transmission main body and electronic control device must function as intended when assembled in a final connected state. Because the connection of an automatic transmission body and an electronic control device is performed at the installation stage, it is impossible to control the automatic transmission main body and electronic control device that are to be connected in a one-to-one correspondence before the installation stage. Therefore, there is a need to adjust the automatic transmission main body and counter-part electronic control device such that they conform to each other after they are installed in a vehicle. Due to the above-mentioned circumstances, total quality control of automatic transmissions is a difficult task requiring many manhours.
The electronic control device is designed to output signals for the hydraulic pressure control device in the automatic transmission main body to speed-shift based on various data stored in the electronic control device, and with information regarding the engine input from an engine control computer. The electronic control device outputs the signals in accordance with signals input from sensors provided on the automatic transmission main body. The sensors are designed to detect various pieces of information regarding the transmission. Therefore, long wire harnesses are required for connecting the electronic control device and automatic transmission. The long wire harness results in an increase in cost, an increase in the occurrence of electronic noise and an increase in the number of manhours needed for wiring and wire-bundling. Moreover, a significant amount of space is required for the wiring.
To avoid these drawbacks, an attempt has been made to put an automatic transmission main body and an electronic control device in a one-to-one correspondence by combining the components into a single unit. For example, Japanese Patent Publication No. Hei 5-70023 discloses an automatic transmission main body and an electronic control device combined by incorporating the electronic control device into the case of a position detecting switch. The position detecting switch is conventionally disposed on an automatic transmission casing for outputting an electric signal to the electronic control device indicating a range position chosen by a driver during a selecting operation.
However, the mere integration of the two components into a single unity as disclosed in the above-mentioned example, results in several drawbacks. Because the engine, automatic transmission and other devices are located close to each other in the engine compartment of a vehicle, placing a large-size component, such as the integrated components, on the outside of the automatic transmission casing interferes with other devices. To avoid interfering with the other devices, the integrated components disposed on the outer surface of the automatic transmission casing need to be compact. However, in the above-mentioned example, the electronic control device is merely placed inside the case of the position detecting switch with no particular consideration taken with regards to the problem of space within the engine compartment.
Since the position detecting switch is designed to detect an operational position of a manual valve disposed in the hydraulic pressure control device based on the rotational displacement of a manual shaft linked to the manual valve, any deviation between the position of the manual valve and the range position detected by the position detecting switch must be eliminated. Therefore, an operation of establishing precise conformity in the positional relationship between the two components, that is, range position alignment, is required during assembly. To perform the range position alignment, typically the manual shaft linked to the manual valve and the rotor of the position detecting switch are first connected in a manner that prevents relative rotation thereof. Next, the position detecting switch case is turned around the shaft of the rotor until the range position indicated by the position detecting switch conforms to the position of the manual shaft. The case is then fixed to an outer surface of the automatic transmission casing by bolts or the like. As such, space must be allotted to mount the position detecting switch on the automatic transmission casing, as well as space that allows the rotation of the case around the shaft, in addition to space to be occupied by the external shape of the case. That is, the space required to mount the position detecting switch inevitably includes a dead space that is no longer needed after range position alignment is established.